Method of producing cumene hydroperoxide

ABSTRACT

The specification provides a method of producing cumene hydroperoxide by continuous aqueous-emulsion oxidation at a high temperature and pressure in a cascade of reactors, wherein the process is conducted in the presence of a mixture of an aqueous solution of an ammonium salt with a concentration of 0.001-0.5 mass % and an aqueous solution of ammonia with a concentration of 0.001-0.5 mass %, which mixture is fed into each oxidation reactor in an ammonia:ammonium salt mass ratio of 1:100 to 100:1.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 10/629,189 filed Jul. 29, 2003; which is a U.S. non-provisionalapplication based upon and claiming priority from Russian ApplicationNo. 2002120653/04 (021637), with a filing date of Jul. 29, 2002, asamended on Jun. 11, 2003, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates to the field of petrochemical synthesis, i.e. tothe technology of oxidation of cumene by an oxygen-containing gas(usually by air) to form cumene hydroperoxide (CHP) whose subsequentdecomposition in the presence of an acid affords phenol and acetone.These reactions are the typical scheme for industrial heavy-tonnageproduction.

Two primary methods of producing cumene hydroperoxide (CHP) are known.

The first, so-called “dry” method is based on liquid phase oxidation ofpure cumene conducted in the presence of catalytic amounts of basiccompounds, e.g.:

-   carbonates of alkali and alkaline-earth metals [See, e.g., U.S. Pat.    No. 2,613,227 (1952), U.S. Pat. No. 2,619,509 (1952), U.S. Pat. No.    2,689,936 (1954)],-   sodium bicarbonate [See, e.g., U.S. Pat. No. 2,577,768 (1951)],-   calcium hydroxide [See, e.g., U.S. Pat. No. 2,632,774 (1953)],-   barium oxide [See, e.g., U.S. Pat. No. 4,153,635 (1979)],-   substituted ammonium salts [See, e.g., U.S. Pat. No. 4,192,952    (1980)], and other compounds that, in the process of oxidation, are    suspended in cumene.

The use of such basic compounds is advantageous for the followingreasons. In the process of oxidation of cumene, trace amounts of organicacids, particularly formic acid, are formed along with the targetproduct, CHP, and two main impurities, acetophenone (ACP) anddimethylphenylcarbinol (DMPC). The presence of formic acid in the cumeneoxidation reaction mass inevitably leads to acid-catalytic decompositionof CHP with formation of phenol and acetone. It is known that phenol isa strong inhibitor of the free-radical oxidation of alkylaromatichydrocarbons and cumene in particular. Thus, the presence of even traceamounts of formic acid significantly slows the oxidation process rate.Therefore, efforts are made to conduct the cumene oxidation reaction atpH˜5-7. The most obvious technique for removing acids from the cumeneoxidation reaction mass is to conduct this process in the presence ofthe aforementioned advantageous basic compounds.

The second, so-called “wet,” aqueous-emulsion method of producing cumenehydroperoxide by oxidation of cumene consists of conducting theoxidation reaction in a three-phase system including:

-   an organic phase consisting of cumene and the products of its    oxidation,-   an aqueous phase consisting of solutions of basic compounds, and-   a gaseous phase consisting of an oxygen-containing gas (usually    air).

Both the “dry” and the “wet” cumene oxidation methods are conducted inthe presence of basic compounds.

Basic compounds dissolve in water much better than in hydrocarbons.Therefore, the mass transfer process in heterogeneous “organicphase-water” systems is much more effective than in “organic phase-soliddispersion” systems. So, in terms of the more complete and fasterremoval of acids from the system, the “wet” oxidation method should berecognized as more effective than the “dry” method.

This invention specifically relates to the “wet” method of cumeneoxidation.

A method is known for producing CHP by oxidation of cumene by air at ahigh temperature. The oxidation reaction is conducted in the presence ofammonium salts of organic acids or carbonic acid; 0.05-50% aqueoussolutions of the salts are used. The method (USSR Author's CertificateNo. 567723, published on Sep. 9, 1977 in Bulletin of Inventions No. 29)has the following disadvantages, which are first discuss with examplesusing ammonium salts of organic acids. Under high-temperature (80-120°C.) conditions of the cumene oxidation process, partial thermaldecomposition of the salts occurs by the following reaction:

where: A is the symbol of an organic anion,

-   -   AH is the symbol of the acid of that organic anion.

Since ammonia features a significant volatility, the liquid phasepredominantly contains the acid that inhibits the cumene oxidationprocess. Moreover, it is economically inefficient to use ammonium saltsof such relatively expensive organic acids as ethylenediaminetetraaceticor 1,10-decanedicarbonic acid.

If ammonium carbonate, an ammonium salt of carbonic acid, is used, thenunder high-temperature conditions, decomposition of the salt occursaccording to the following reaction mechanisms:

Reaction (1) predominately occurs in the aqueous phase while reaction(2) dominates in the organic phase.

An increase in the temperature shifts the equilibrium in Reaction (1) tothe right while a decrease in the temperature shifts it to the left.Industrial cumene oxidation reactors are equipped with condensationsystems whose function is to condense the carryover vapors of cumeneand, partially, of water. In the condensation process that is conductedunder lower temperature conditions, the equilibrium in Reaction (1), asmentioned above, shifts to the left, which results in a partial recoveryof the alkaline agent in the cumene oxidation reactor. That circumstancehas a positive effect on the process performance. On the other hand,Reaction (2) eventually leads to formation of carbamide (urea) whoseaqueous solution has a much lower pH than the corresponding ammoniasolutions. That circumstance inevitably leads to a worsening of thecharacteristics (rate and selectivity) of the oxidation process.

Furthermore, the salts are practically insoluble in organic phases whilethe volume of the organic phase represents the larger part of thesolution. That is why the salts clog the pipelines and precipitate onthe walls of heat-exchanging equipment, which leads to reduced heattransfer coefficients. This circumstance especially impairs the processof CHP rectification/concentration that follows the cumene oxidationstep.

As follows from the description of invention (Author's Certificate No.567723), that process is essentially a “dry” oxidation process since theamounts of the aqueous solutions added are so small (e.g., 50% solutionsof ammonium carbonate are used in an amount of 0.17 g per 300 g ofcumene) that all water is dissolved.

A process is known for producing cumene hydroperoxide using air oxygenin the presence of gaseous ammonia in the amount of no less than 0.5% ofthe reacted oxygen [U.S. Pat. No. 2,632,026 (1953)]. Although the cumeneconversion (up to 21%) and CHP formation selectivity (up to 97.3%)characteristics of that process are good, its primary disadvantage is avery low oxidation rate.

The process has the following primary disadvantage: in feeding gaseousammonia into the reactor, most of the ammonia escapes into theatmosphere. All existing CHP synthesis plants are equipped withwaste-gas afterburning units (thermal afterburning units are used moreoften than the catalytic ones). This, in turn, leads to the presence ofnitrogen oxides in the gaseous emissions and has a negativeenvironmental impact. Furthermore, the patent's high conversion andselectivity characteristics are achieved at a very low cumene oxidationrate (0.6% cumene per hour). In its technical essence, the closestprototype of the proposed method is a process for producing cumenehydroperoxide by oxidation of cumene in an aqueous/alkaline emulsion ata temperature of 92-107.2° C. and a gage pressure of 5 atm in ahorizontal cascade of reactors (no fewer than two) in two steps: cumenesequentially passes the first-step and second-step reactors into each ofwhich the oxidant (air) is fed. In order to neutralize the acids, anaqueous solution of sodium carbonate is fed into the second step of theprocess; in the course of neutralization, sodium carbonate istransformed into sodium bicarbonate. The aqueous salt solution from thesecond step of the process is treated by ammonia or ammonium hydroxideup to pH=10.5-11.5; in the course of that process, sodium bicarbonate istransformed into the mixed salt, NH₄NaCO₃. The neutralized solution isfed into the first-step reactors in a ratio of (3.5-2.6):1 to the cumenethat is fed for oxidation [U.S. Pat. No. 5,767,322, 1998: prototype].

U.S. Pat. No. 5,908,962, 1999, held by the same applicant, proposes,under the conditions similar to U.S. Pat. No. 5,767,322, feeding ammoniain an amount at least stoichiometric in relation to the amount of acidsformed in the cumene oxidation process while monitoring the salts thusformed under ambient pH of 10.0-12.0 while ammonia is injected directlyinto the first-step reactors.

It is known that, in oxidation of cumene, two byproducts,dimethylphenylcarbinol (DMPC) and acetophenone (ACP), are formed alongwith CHP; the amount of those byproducts determines, ultimately, theyield of commercial products and the mass of the undesirable productionwaste, the phenolic resin; it also complicates the process of producingcommercial products of the required quality. Therefore, an improvementof the cumene oxidation selectivity at a sufficiently high conversion(optimal CHP concentration in the flow leaving the oxidation unit is25-30%) is an important issue for increasing the effectiveness of theindustrial technology.

The following disadvantages of the prototype process can also beindicated:

-   using different neutralizing solutions for the first and second    oxidation steps, which complicates the technological scheme;-   the presence of sodium salts, which can precipitate on the walls of    heat-exchanging equipment;-   leads to reduced heat transfer coefficients;-   furthermore, the large amount of the neutralizing aqueous solution    in relation to the cumene that is being oxidized, (3.5-2.6):1.    Providing for a required capacity of the oxidation plant results in    larger reactor volumes compared to the “dry” oxidation method.

SUMMARY OF INVENTION

The aim of this invention is to simplify the technology whilemaintaining the high selectivity and rate of cumene oxidation withoutimpairing the environmental characteristics of the process. This aim isachieved by producing cumene hydroperoxide in a series of oxidationreactors wherein the process is conducted in the presence of a mixtureof an aqueous solution of an ammonium salt having a concentration of0.001-0.5 mass % and an aqueous solution of ammonia having aconcentration of 0.001-0.5 mass %, which mixture is fed into eachoxidation reactor in an ammonia:ammonium salt mass ratio of between1:100 to 100:1.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic illustration of an apparatus employed in a cumeneoxidation method of producing cumene hydroperoxide.

DETAILED DESCRIPTION

The process of continuous aqueous-emulsion oxidation of cumene ispreferably conducted in a cascade of flow-through reactors by bubblingair through a water-cumene emulsion. The process is conducted at atemperature of 100-120° C. in the first oxidation reactor of the seriesof oxidation reactors with a gradual decrease to 80-90° C. in the lastoxidation reactor of the series of oxidation reactors and at a gagepressure of up to 5 atm. For example, the process is conducted at atemperature of 120° C. in the first reactor, lowering it to 80° C. inthe last reactor, and at a gage pressure of 5 atm, in the presence of amixture consisting of a 0.007-0.5% aqueous solution of ammonia and a0.001-0.5 mass % solution of an ammonium salt (e.g., ammoniumbicarbonate, ammonium carbonate, ammonium carbamate or a mixturethereof). The ammonia:ammonium salt mass ratio is (1:100):(100:1),preferably (1:10):(10:1). The oxidative feedstock is fed into the bottompart of each reactor while the aqueous phase is fed into the top part ofeach reactor. The organic layer of the reaction mass gravity overflowsinto a vessel, from which it is periodically discharged. The aqueousphase is periodically discharged from the bottom of the reactor andflows through valves into a vessel. The gaseous phase is partiallycondensed in a cooler, passes an activated-coal filter, where partialsorption of cumene takes place, and then goes, through control valves,into an oxygen analyzer and rheometer. The discharge rates of the liquidphases are controlled by pumps. The reactor temperature is set by athermostat (oil is used as a heat-carrying agent) and measured by athermocouple.

An essential distinctive feature of the proposed aqueous-emulsionprocess of cumene oxidation is that the process is conducted using amixture consisting of a 0.001-0.5 mass % aqueous solution of ammonia anda 0.001-0.5 mass % solution of an ammonium salt (ammonium bicarbonate,ammonium carbonate, ammonium carbamate or a mixture thereof) at anammonia:ammonium salt mass ratio of (1:100):(100:1), preferably(1:10):(10:1).

The utilization of ammonium salts such as ammonium bicarbonate asneutralizing agents in the cumene oxidation process makes it possible tosubstantially simplify the process technology, at a process selectivityof ˜94% or better and a conversion of 23%, by excluding the use ofneutralizing agents that form solid deposits on heat-exchangingequipment.

A representative apparatus for practicing the process according to theinvention is shown in FIG. 1.

The industrial applicability of the proposed method is confirmed by thefollowing examples.

EXAMPLES 1-6

The basic experiment parameters (a pressure of 5 atm and a temperatureof 80-120° C.) simulate the working conditions of the individualreactors of an actual industrial plant. The feedstock flow rate wasselected in such a manner that the CHP concentration gain correspondedto a six-reactor system.

In the experiments, cumene of a purity of no less than 99.85% was used.The aqueous phase was prepared from ammonium bicarbonate of the“chemically pure” grade with an ammonia content of no less than 21.7%.

The oxidative feedstock for each of the experiments was either purecommercial cumene (first reactor, T=120° C.) or oxidation productsobtained in the course of the previous experiments.

The concentration of CHP was determined by iodometric titration.

The concentrations of ACP and DMPC were determined by gas-liquidchromatography: a chromatograph with a flame ionization detector and a25 m long column with an outer diameter of 0.32 mm; stationary liquidphase: OV-1; T_(initial)=50° C., temperature rising rate: 8° C./min,T_(final)=20° C. The quantitative calculations were performed usingn-pentadecane as the internal standard.

The aqueous phase flowrate was 6-7 ml/hr while the oxidative feedstockflowrate was 200-260 ml/hr.

In order to simulate the operation of an actual six-reactor industrialplant, temperatures falling into the range of 120-87.8° C. were selected(see Table 1). For the first reactor (T=120° C.), pure commercial cumene(C_(CHP.0)=0.07%) was used as the oxidative feedstock. In the subsequentexperiments, the products obtained in the course of the previousexperiment were used as feedstock.

The experiments were conducted as follows. In the atmosphere ofnitrogen, the reactor was filled, until liquid overflowed into thevessel, with the oxidative feedstock and 20 ml of the 0.001-0.5 mass %aqueous solution of the ammonium salt and the reactor heating was turnedon. After the required temperature was reached, the nitrogen flow wasstopped and air feeding was started. In 1 hour, the first sample of theorganic phase was taken through a siphon tube and analyzed for CHPcontent. In another hour, the second sample was taken and sampling wasdone in that manner until the expected CHP concentration was reached.After that, the pumps were turned on and in 12-15 hours the steady modewas established. The aqueous phase was periodically (every 0.5 hours)discharged from the bottom of the reactor. The organic phase wascontinuously overflowing into a receiving vessel that was dischargedperiodically. After a steady mode was reached, organic phase sampleswere taken every 3-4 hours and analyzed for the content of CHP(titration) as well as the contents of DMPC and ACP (gas-liquidchromatography). The duration of each experiment was 24 to 72 hours.

The ammonium salt concentration for each of the experiments was selectedexperimentally. It has been found that, for each of the simulatedreactors, there exists an optimal concentration below which theoxidation reaction rate falls significantly while, at higherconcentrations, a decrease in selectivity is observed.

The data thus obtained for experiments 1-6 respectively are shown inTable 1. Concentration, mass % Cumene Selectivity of pH of pH ofAmmonium C_(CHP.0), C_(CHP), conversion, CHP aqueous org. T° C. saltAmmonia % % % formation, % phase phase 120.0 0.001 0.005 10.07 6.41 5.2395.6 6.7 6.2 102.0 0.005 0.007 6.41 11.62 5.01 95.0 6.9 6.3 98.0 0.0150.005 11.62 17.63 4.76 94.7 7.0 6.9 94.4 0.03 0.05 17.63 22.20 3.80 94.07.3 6.4 91.0 0.08 0.02 22.20 24.75 2.48 92.7 7.2 6.3 80.0 0.04 0.0824.75 28.8 3.40 92.5 7.3 6.3

EXAMPLE 7

The process is conducted similarly to examples 1-6 but, in oxidation, anaqueous solution of an ammonium salt obtained by passing carbon dioxidegas through an aqueous solution of ammonia is used. At an oxidationtemperature of 120° C. and a pressure of 5 atm, the conversion is 5.3%and the selectivity was 85.7%.

1. A method of producing cumene hydroperoxide comprising: reacting in aseries of oxidation reactors oxygen with cumene by passing the oxygenthrough a water-cumene emulsion in a presence of a mixture of an aqueoussolution of an ammonium salt with a concentration of 0.001-0.5 mass %based upon a total mass of the aqueous solution of the ammonium salt andan aqueous solution of ammonia with a concentration of 0.001-0.5 mass %based upon a total mass of the aqueous solution of the ammonia, whereinthe mixture is fed into each oxidation reactor of the series ofoxidation reactors in an ammonia:ammonium salt mass ratio of between1:100 to 100:1; wherein the ammonium salt is selected from the groupconsisting of ammonium bicarbonate, ammonium carbonate, ammoniumcarbamate, and a mixture thereof; and decomposing the cumenehydroperoxide acid and a phenol.
 2. A method according to claim 1,wherein the method is conducted at a temperature of 100-120° C. in afirst oxidation reactor of the series of oxidation reactors with agradual decrease to 80-90° C. in a last oxidation reactor of the seriesof oxidation reactors and at a gage pressure of up to 5 atm.
 3. Themethod according to claim 1, further comprising forming the ammoniumsalt by reacting carbon dioxide with ammonia in the presence of anaqueous feed stream for one of the oxidation reactors of the series ofoxidation reactors.
 4. The method according to claim 1, wherein theammonia:ammonium salt mass ratio is 1:10 to 10:1.
 5. The methodaccording to claim 1, wherein the oxygen is from air.
 6. A method ofproducing cumene hydroperoxide comprising: reacting in a series ofoxidation reactors oxygen with cumene by passing the oxygen through awater-cumene emulsion in a presence of a mixture of an aqueous solutionof an ammonium salt with a concentration of 0.001-0.5 mass % based upona total mass of the aqueous solution of the ammonium salt and an aqueoussolution of ammonia with a concentration of 0.001-0.5 mass % based upona total mass of the aqueous solution of the ammonia, wherein the mixtureis fed into each oxidation reactor of the series of oxidation reactorsin an ammonia:ammonium salt mass ratio of 1:10 to 10:1, wherein themethod is conducted at a temperature of 100-120° C. in a first oxidationreactor of the series of oxidation reactors with a decrease to 80-90° C.in a last oxidation reactor of the series of oxidation reactors and at agage pressure of up to 5 atm, and wherein the ammonium salt is selectedfrom the group consisting of ammonium bicarbonate, ammonium carbonate,ammonium carbamate, and a mixture thereof; and decomposing the cumenehydroperoxide acid and a phenol.
 7. A method of producing cumenehydroperoxide, comprising: forming ammonium salt by reacting carbondioxide with ammonia in the presence of an aqueous feed stream; andreacting oxygen with cumene by passing the oxygen through a water-cumeneemulsion in a presence of a mixture of the ammonium salt and theammonia; wherein the mixture is fed in an ammonia:ammonium salt massratio of 1:100 to 100:1; and decomposing the cumene hydroperoxide acidand a phenol.
 8. The method according to claim 7, wherein the ammoniumsalt is selected from the group consisting of ammonium bicarbonate,ammonium carbonate, ammonium carbamate, or a mixture thereof.
 9. Themethod according to claim 7, wherein the ammonium salt comprisesammonium carbamate.
 10. The method according to claim 7, wherein theammonia:ammonium salt mass ratio is 1:10 to 10:1.
 11. The methodaccording to claim 7, wherein the method is conducted at a temperatureof 100-120° C. in a first oxidation reactor with a gradual decrease to80-90° C. in a last oxidation reactor, and at a gage pressure of up to 5atm.
 12. The method according to claim 7, wherein the mixture of theammonium salt and ammonia comprises an aqueous solution of the ammoniumsalt with a concentration of 0.001-0.5 mass % based upon a total mass ofthe aqueous solution of the ammonium salt, and an aqueous solution ofthe ammonia with a concentration of 0.001-0.5 mass % based upon a totalmass of the aqueous solution of the ammonia.
 13. The method according toclaim 7, wherein the reacting of the oxygen with the cumene is in theabsence of a neutralizing agent that forms a solid deposit onheat-exchanging equipment.
 14. The method according to claim 13, whereinthe neutralizing agent comprises sodium salt.
 15. The method accordingto claim 1, wherein the reacting of the oxygen with the cumene is in theabsence of a neutralizing agent that forms a solid deposit onheat-exchanging equipment.
 16. The method according to claim 14, whereinthe neutralizing agent comprises sodium salt.
 17. The method accordingto claim 1, further comprising forming the ammonium salt by reactingcarbon dioxide with the ammonia.
 18. The method according to claim 1,wherein the ammonium salt is ammonium carbamate.